Optimization for solderability of large-size single-crystal diamond with heterogeneity alloys by tantalum coating

Abstract

To ameliorate the solderability of single-crystal diamond with heterogeneity metals/alloys, tantalum (Ta) coatings were prepared on the diamond by utilizing the double glow plasma surface metallurgy (DGPSM) technique. Using Ag-Cu-Ti solder, the Ta-coated single-crystal diamonds were soldered onto cemented carbide (WC-Co) matrixes. The effects of metallization temperatures on the microstructure, phase, and solderability of the Ta-coated diamond were investigated. The results show that uniform and compact Ta coatings with increased thicknesses are obtained with increasing metallization temperatures. Besides, under all the temperatures, the diffusion layers composed of Ta2C and TaC could be formed at the Ta/diamond interface, which is beneficial to enhance the coating adhesion. The average shear strength of the soldered joint with Ta-coating increases first and then decreases with the increase of temperature. The maximum value is 118.7 MPa on the soldered joint with 850 °C Ta coating, which is approximately 57% higher than without Ta coating. Three failure modes occur during the shear process, including the ductile fracture of the soldered seam, brittle fracture in the interior of Ta carbides at the Ta/diamond interface, and brittle fracture of the single-crystal diamond itself. Among them, the ductile fracture of the soldered seam is the dominant fracture mode.